Lovely little trick of German Engineering
For the past two months or so of driving my 1995 Jetta, I've dealt with brakes that can only be categorized as somewhat sketchy.
A quick review: I replaced all the rear hardware minus drums and wheel cylinders before putting the car on the road- both sides had seized. I also replaced front rotors, but could not run the new brake pads I had bought; they were the right shape, but about 3mm too thick to fit between caliper and rotor, even with the piston fully compressed. Oh, also AAP has a $3 destination fee for ordered in parts that they will not refund for returned parts that came from the hub five miles down the road. So I slapped some used pads with good life left in them and sent it down the road.
A few weeks and several hundred miles later, I put pads from RockAuto on. Here's where the fuckening begins. Bedding in brakes, to those who are unaware, requires several hard stops from 35 to 0, then a few from 50-60 down to 15 or so. I don't really understand the magic that happens, but when you do this you get better brake performance versus just putting pads in and driving as normal. Anyways, lots of hydraulic pressure and old rubber seals in a master cylinder don't tend to get along very well, and generally the non-compressible liquid will win the fight against some o-rings, and you're left with no brakes. Luckily, VW designed the brake system very well on this car- there are two circuits, which cross the car, so you can still stop even with half the brakes not working. So, I parked it and ordered a new master cylinder. RockAuto and FedEx shoved their thumbs up their asses and took almost two weeks to get a part from Indiana to Ohio. I could have just walked there and it would have been quicker.
Slap it back together, drive a few hundred more miles, oh no, now my brake fluid level is dropping! What the hell!
More rubber seals had retired. This time, the passenger side wheel cylinder. Wait another two weeks for RockAuto and FedEx to get me a $3 part. Install it.
Not having a cap nut on hand, I lost about an ounce and a half of brake sauce out of the hard line. That's fine, bleeding brakes isn't too hard.
Oh wait! Here's the titular trick of German Engineering- a dynamic self-adjusting brake bias valve. It looks like this:
These cars have a pretty soft suspension with lots of travel, which allows you to do things like this:
However, in a hard stop in a straight line, the rear wheels will naturally unload and weight will shift towards the front wheels. With a static brake bias an no ABS, this means the rear wheels will have too much braking force and will lock up, sending you into a spin. This is why VW put this bias valve in- it mounts between the floor pan and the torsion beam. As the beam moves away from the floor under hard braking, a piston moves out, reducing brake force to the rear. A clever solution to the problem. I can't think of any other manufacturer who does this, though my experience is pretty limited.
This system ceases to work correctly under a few situations- old worn out seals in the valve (which has yet to happen to me), and lowered cars (weight still shifts even if the suspension doesn't travel much) are the main ones. It also makes a relatively routine task a huge pain in the ass.
Because suspension travel limits the flow of brake fluid, you cannot simply jack the car up to bleed the brakes. You must elevate the car by the wheel. All four wheels must be the same distance from the ground. And no, there really isn't enough ground clearance to do this with the car resting on the ground.
My preferred method- jack up the car one corner at a time, and set the wheel on a car ramp. Now you have about a foot more clearance to get at the wheel cylinders.
Cool, now throw a wrench on the bleeder and turn it open. You need to turn it about 1/4-1/2 a turn to "open" them on these for whatever reason. Problem: the wheel is still on the car, and the placement of the bleeder means you can get maybe an eighth of a turn before you hit the wheel.
I've done it a few times and never revel in it. The lack of wrench turning space also makes solo bleeding kind of terrible. You can't just leave the wrench on and close the valve with a hose still on the nipple- you must remove the hose with the valve still open. This lets a teeny tiny bit of air get in, so the first 10% of brake pedal travel is soft. I really need a speed bleeder.
Thanks for reading my ramblings on brakes breaking. Here's everything left to do on this car:
- Brake hoses (unknown age on the car, but no signs of dry rot or imminent failure. I know that's not how this works)
- Fix the washer sprayers
- Hunt down the wiring issue for the distributor (car doesn't advance spark timing. Am probably working with 75 hp at most right now)
- Fix some interior trim
- Flush gear oil, or just ignore it. It's only got 90k miles, but the car sat a few years outside before I got it. What say you, Oppo?
- Replace the last of the shifter bushings- getting into 1st requires slamming it from 2nd, but the bracket holding the bushing in question is very seized.
- Fix lights in the instrument cluster and intermittent speedometer functionality (is it really only 90k miles?)
- Get AC working
- Replace HVAC blend door (dash out! That's why I haven't done it)
- Replace front strut bearings- intermittent creakiness
functionoverfashion last edited by
Sounds about par for the course for a '95 Jetta. But that brake biasing valve does sound like a neat idea!
Sounds about par for the course for a '95 Jetta. But that brake biasing valve does sound like a neat idea!
It is cool. I'm swapping my Golf over to rear disc in the nearish future, which means I have to swap out the valve for a different one that biases differently since discs require more fluid to be pushed than drums. The downside of a cool somewhat intricate mechanism is that they're like $120 minimum, more than the hoses, calipers, stub axles, and other hardware for the swap cost. But it's necessary, as I drive the car a lot harder than most people who do the swap for looks.
Mark Tucker last edited by Mark Tucker
As far as I know, nearly every car has some sort of proportioning valve for the brake bias. They balance out the hydraulic pressure when weight shifts forward, exactly as you describe. Most work off the hydraulic pressure in the lines.
The one you're describing sounds like what's called a load-sensing valve, which is intended to shift bias towards the rear when the rear suspension is sitting lower (ie, when there's a heavy load in the back). They're not uncommon on pickups/SUVs, especially the heavier-duty ones. My 1991 Nissan Pathfinder had one, but I never had to mess with it. I didn't know that VW used them on these; I'm pretty sure my Mk1 and Mk2 VWs did not have a load-sensing valve.
As far as bleeding it goes, I would imagine that the easy way would be to jack the car up, disconnect the arm of the valve from the suspension, and use something to hold it open manually while you bleed the brakes, is that not possible?
Not at all an unusual thing to have a biasing valve on older cars.
Most modern cars don't have them anymore, instead relying on ABS systems to do the biasing for them. This has the interesting effect on later model VWs where if one is a light braker, the rear pads wear out first because the ABS biases to engaging the rear first, then as you apply more and more pressure it clamps down harder on the front.
I will also say specifically on VW's products with ABS, 1995 and older ABS equipped VWs still have that unloader valve. They used the ATE "MK4" system through the '95 model year. The ATE MK4 has a bug ugly accumulator next to the master cylinder and the control module lives under the driver side rear seat on the Passats.
Come model year 1996, they switched to the ATE MK20 system, the unloader valve goes away, the master cylinder only has 2 outlets instead of 4 and the control module is bolted directly to the valve block, the whole assembly still being next to the master cylinder.
I will also say this much, the combination of different master and having the MK20 system do the brake biasing instead of the unloader valve makes the pedal effort easier to apply serious stopping power.
Qaaaaa last edited by Qaaaaa
@mark-tucker Yeah, load sensing is what it is. Couldn't remember the words.
The Mk2 I briefly had did not have a valve like this. My Cabriolet, built in Germany, does, I think, but my Rabbit does not- there is a manually adjustable valve in the engine compartment. I think that was only installed on 1981-85 Westmoreland built Rabbits.
Disconnecting the valve from the suspension would be a lot harder than jacking up and setting the wheels on a ramp I think. Old bolts, non-galvanized steel and all...
@dieseldub what had ABS pre 95 besides Passats? I thought Jetta GLX/GTI VR6 was only ABS in OBDII, did Corrados get it?
dieseldub last edited by dieseldub
@qaaaaa Also for fun, here's a photo of my first VW back in 2009 (I owned it since 2004). 98 Mk3 Jetta TDI doing the usual VW 3 legged/dog salute:
That was a GREAT car. It had the rear drums as well, no ABS. I did eventually do the rear disk conversion. Conversion was done before I went to this track day.
Also bummed that Borbet doesn't make the Type B/CBs anymore. They looked great on the mk3. Really clean design.
@qaaaaa I think anything that had a VR6 got it, but I could be wrong on the Jetta GLX pre-96.
I don't think the hatch even got the VR6 until OBD2. I know I've heard of Corrado SLCs with it, but unsure on if they all had it or not or if it was just an option.
I had a 95 Passat wagon VR6 that was converted to TDI that had the ATE Mk4 in it.
@dieseldub Oh man that pic is awesome. Some of my friends have started going to track days (if you're reading this, hi Dimitri) and I intend to get my Golf back on the road and track it. Rear drums were predictably terrible when I took the car to the Tail of the Dragon, so the disc swap is in order. I'm going to keep Mk2 GTI snowflakes/Avus on until I don't have enough brakes, then do the Girling 60 brake swap, which requires 15s.
There's a guy near ish to me that has an SLC roller. I think he wants like $1200 for it. It is very, very tempting to snatch it and throw something into it. Probably ABA/16v turbo and an 02M.
@qaaaaa I'm very much a fan of the 5 lug swap. Usually sourcing the parts from Pick n Pull.
Different sway bar, control arms, knuckles, axles, ball joints, calipers.
The 288 mm setup is great, the suspension geometry gains you about a degree of caster, if you get the later Mk3 VR6 parts you get a really, really nice sway bar setup. Reduces how much roll the front end has nicely. Not to mention the additional whoa from those brakes--but speaking from experience, it's nicer to drive with the full ABS--which probably isn't a worthwhile swap time-wise or cost wise to replace EVERY SINGLE BRAKE LINE to do it.
The AHU drivetrain in this black Jetta eventually got transplanted into a '97 GLX and I put a set of early GLX BBSes on it. LOVED that setup. I might have mentioned that swap before in previous posts with you. I can't remember.
@dieseldub I can't remember if you'd told me that, you've probably had more VWs than I have.
I have seen a single VR6 Mk3 in a junkyard ever, and it was a four lug swap car. Five lug swap won't be doable without that. I've priced it from RockAuto and... sheesh.
I don't think I'd even be able to use axles from a four lug. As far as I know, the splining is different, plus they're too short. And it's not really a worthwhile swap IMO on my particular cars, since they're kind of shitty to start with. I have a set of Koni sports and some Eibach sport lines I got on black friday sale ($106 shipped for the set!) so hopefully that will make turn and roll in a little nicer.
@qaaaaa starts thinking back and counting
17 that I can remember. 18 if I include the 91 Jetta ECODiesel that a previous owner swapped a 16V into, but I never received the title for it and eventually sold it back to the guy.
3 MK2s in that list (89 GTI 16V, two 91 Jettas--3 91 Jettas if you include that 16V-swapped ECODiesel I never got the title for),
2 mk3s (my original 98 TDI, and then the '97 GLX I swapped the TDI into),
2 B4 Passats (one sedan, one wagon--both TDIs, the wagon was originally a VR6).
3 05 Passat wagons (all BHW powered)
2 99.5 Golf 2 door, crank window ALH, German-built
1 01 Golf Brazil built--4 door power windows, ALH
2 03 Jetta wagon ALHs
1 00 New Beetle ALH
1 04 Touareg V10 TDI (BKW)
1 14 Passat TDI (CKRA)
Only 1 that was a gas-powered VW the entire time (the GTI).
2 that started life with a VR6 but got TDI transplants ('97 Jetta was done by me, the '95 Passat wagon I bought already 'converted' and had to fix a lot of the half ass things done with the swap by "Nice Cars Inc")
I'm pretty sure that's all I've had.... pretty sure... glances side to side suspiciously expecting another VW to show up that I forgot about
@dieseldub ...holy shit that’s a lot of TDIs. I’ve had/have (ignoring non VWs): 1981 Rabbit Diesel, 1986 Cabriolet, 1987 Audi 4000S, 1991 Jetta (eco diesel on the title, German built, but had an 87 ish turbodiesel swapped in), 1995 Jetta, 1996 Golf, 2001 Golf. The Mk3s are all 2.0, the Audi and Cabby are 1.8s.
@qaaaaa I forgot one... I had a 2006 Jetta mk5 with the BRM in it. Lol
That's a nifty list of VAG. Kind of getting excited to get this mk2 project on the road. Haven't had a proper old school VW FWD in awhile.
DipodomysDeserti last edited by DipodomysDeserti
@qaaaaa My 2001 Tundra has a "load sensing proportioning valve". It uses a rod to "sense" increased load in the bed and increases braking force to the rear. It has very good brakes for a twenty year old pickup truck with no ABS or TC.
Qaaaaa last edited by Qaaaaa
@dieseldub I’m honestly on the edge with this Jetta. I’m kind of sick of daily it. Super slow with whatever wiring issue it has (you got a spare OBDI harness laying around?) and with crap heat it sucks in Ohio. I was gonna snag a 200k mile Mk6 2.slow at Copart but it got bid up to $1100 by some dude in Mexico. I think what I miss the most about modern cars is heated mirrors.
I’d try and get a Mk4 with an ALH but I just hate the interior on those so much. They feel pretty numb to drive IMO. And high mile PDs scare me, unless they were deleted when young. Some buddies have them and horror stories are common.